The effect of the blend composition on the thermal diffusivity for blends of a poly(ethylene-co-cyclohexane 1,4-dimethanol terephthalate) (PETG) and a bisphenol-A polycarbonate (PC) that have been used as base films for a thermal dye transfer (TDT) printing system was examined. The inflection point in the thermal diffusivity measured by temperature wave analysis almost matched the inflection point of storage modulus measured by dynamic mechanical analysis. This result implied that the temperature dependence of thermal diffusivity related to the change in the microstructure of the PETG/PC blend. Furthermore, the correlation between the printing sensitivity and the thermal diffusivity at the actual thermal head temperature of TDT printing was found. The thermal diffusivity increased with increasing PC content, while the printing sensitivity decreased. The PETG/PC blend film suitable for the TDT printing base film could be obtained by adjusting the PC content in the blend. (C) 2004 Wiley Periodicals, Inc.